Coronary heart disease (CHD) is a major cause of death and disability. Risk factors have been detected in children. Evidence suggest that habitual physical activity offers partial protection against primary and secondary events of CHD. Consequently, it has become important to include a measure of cardiorespiratory fitness in epidemiological studies of heart disease or other aspects of preventive medicine. Whereas maximal exercise tests are the accepted standard in measuring cardiorespiratory fitness, their use is difficult, especially in epidemiological studies. A key question is whether a more simple fitness test with satisfactory accuracy, precision and safety can be used in measuring fitness. Step tests with differing heights, stepping rates and methods of counting recovery heart rate have been used in the past for adults. However, the applicability of these tests to diverse populations, including children, is limited and further development has been neglected because of the appeal of high technology studies. Such a practical alternative to the more traditional physiologic tests should be considered. It could be used in the office of a clinician to assess cardiorespiratory fitness level and can be used in health and physical education programs to monitor fitness and intervention programs of children. The long term objective of this study is to develop a step test that has a normalized stepping height and rate which can be used by children (and adults alike) and can be used for epidemiological purposes. The specific aims include: 1) To apply a previously developed anatomical model to at least 10 males and 10 females in each age for children aged 6-18 (260). This model defines the appropriate stepping height as 0.188 times the individual's statute height, which should result in an optimum hip angle of 73 degrees when stepping. 2) To design and construct a variable height stepping apparatus for use in the step test. 3) To design and construct a heart monitor or pulse counter which can count recovery heart rate. 4) To validate the step test by performing direct maximal oxygen consumpton (Bruce Treadmill protocol) of 20 children in each of the following age groups: 6-9, 10-12, 13-15, 16-18, and relating the recovery heart rate of the step test with the measured maximum oxygen consumption. 5) To determine the appropriate stepping rate by finding the best correlation between recovery heart rate and stepping rate by finding the best correlation between recovery heart rate and measured maximum oxygen consumption using two stepping cadences (22 and 26/minute).